The transition has been in the works for some time, a health department spokesman said.

Shah, who was appointed by Governor Andrew Cuomo in 2011, has overseen the governor’s reforms to the state’s $54 billion Medicaid program. He’s also become the target of criticism as the head of the state’s health study on the risks of hydrofracking, which has delayed a decision on whether to lift a moratorium on the controversial drilling practice.

Shah has offered no timeline for a fracking decision, after the administration previously suggested the study was nearing an end.

The news of Shah's departure comes the same day Republican gubernatorial candidate Rob Astorino called for Shah’s resignation, hitting him both for the delay in the hydrofracking study and for a recent New York Post news report that showed the state’s abortion clinics have been infrequently inspected, with many sites going years between safety inspections from the state’s health department.

GOP Assemblywoman Nicole Malliotakis also called for Shah's resignation, according to the
Staten Island Advance.

Shah's departure is a big loss for the Cuomo administration, which declined to comment.

The health department has been put in charge of a number of large projects, including the implementation of a medical marijuana program, the $8 billion Medicaid waiver program, a review of hydrofracking and redesigning the state's Medicaid delivery system.

Zucker is expected to take over all of Shah's duties.

He was appointed in 2013 to a newly created position, and led the department's efforts on issues related to New York City. Zucker, who graduated medical school at 22, was a White House Fellow under then-Health and Human Services Secretary Tommy Thompson, and the Deputy Assistant Secretary of Health, where he developed the nation's Medical Reserve Corps, which today is run by the U.S. Surgeon General and includes more than 200,000 volunteers across nearly 1,000 programs.

Zucker was also the highest ranking American at the World Health Organization and led the chartge against counterfeit medicines. He is also a member of the Council on Foreign Relations, Council for Emerging National Security Affairs, and was a "high-level expert" on public health for NATO.

He also serves on the Board of Directors of the nongovernmental organization that oversees the U.S. National Lab on the International Space Station. He has an M.D. from George Washington University, a J.D. from Fordham University and a LL.M. from Columbia Law School.